The present invention relates to a so-called mark-edge recording in which marks are recorded in certain areas of a recording medium so that their physical property is made different from the other areas to thereby have information associated with both ends of each of the marks.
The present invention is particularly suited to a rewritable high-density information recording method capable of recording information to be repeatedly rewritable. The present invention is also suited to a so-called phase-changing type information recording method in which the physical property of the information recorded areas is made different from the other areas by the phase change of the recorded substance that is caused by changing the temperature of the information recording medium.
A conventional rewritable information recording method is disclosed in, for example, JP-A-63-229625. This method is an optical disk recording method for recording information by modulating the intensity of light.
As shown in FIG. 6, information is recorded in a plurality of sectors 21, each of which has identification information 24 provided at its head in order to indicate the physical position of information. This identification information 24 is used as a reference to be followed by a synchronizing signal portion 22 and an information recorded portion 23 which are recorded as a record unit on the recording medium. At this time, the start position of the record unit is randomly changed in its position at each time of rewriting, thereby increasing the possible number of times of repeated rewriting. In other words, the disk material at the same place within a sector is prevented as much as possible from being deteriorated by repeated rewriting, thereby raising the possible number of times of repeated writing.
FIG. 7 illustrates the relation between the number of times of rewriting and the jitter in the case where the same recording information is repeatedly recorded. Here, the jitter is defined as the standard deviation normalized by a reproduction detection window width, the standard deviation being of the time shift between a reproduction clock and a reproduced data after the same random data is EFM-modulated, recorded repeatedly and then reproduced.
In FIG. 7, a curve 701 was obtained when the start position of the recorded portion is shifted by 2 bytes in the mark-edge recording, a curve 702 when shifted by 30 bytes in the mark-edge recording, a curve 703 when shifted by 2 bytes in the mark-position recording, a curve 704 when shifted by 100 bytes in the mark-edge recording, and a curve 705 when shifted by 30 bytes in the mark-position recording. Here, the mark-position recording is the recording system in which information is recorded in association with the center position of the mark.
From FIG. 7, it will be seen that the increase of jitter after rewriting can be suppressed more, or the possible number of times of rewriting is increased as the amount of the shift of the start position of the recorded area is increased. Here, the minimum mark distance, in the mark-position recording in which data is associated with the center position of the mark, was selected to be 0.9 μm, and the minimum mark distance, in the mark-edge recording in which data is associated with both ends of the mark, was chosen to be 0.6 μm. In addition, the diameter of the recording and reproducing spot was 0.9 μm, and the recording medium used was a GeSbTe-based phase-change recording medium.
However, in the start-position shift system, and particularly in the mark-edge recording, the shift of the start position of the randomly recorded data must be increased to about 100 bytes in order to achieve a practical possible number of times of rewriting, as will be understood from FIG. 7, when the same information is repeatedly rewritten. Therefore, the utilization efficiency of sectors was greatly reduced. In addition, under this great positional shift, the beginning end or last end of recorded information will be superimposed upon other recorded portions. Since the recording characteristics of the beginning end or last end of recorded information are deteriorated probably due to the dissolution or flow of the recorded film, the effect of the change of the recording and production characteristics may be expanded over a wide range by repeated rewriting of these portions.